1. Field of the Invention
This invention generally relates to scanning heads. More particularly, the present invention relates to improvements in a contact-type scanning head which, in use, is held in pressing contact with a platen.
2. Description of the Prior Art
As is well known, contact-type scanning heads include thermal printing heads which are widely used in facsimile machines to print transmitted information on thermosensitive paper, and contact-type image sensors which are used to read images carried on paper in close proximity thereof. Because of similarity in arrangement, the thermal printing head and the contact-type image sensor have certain requirements in common.
For conveniently explaining the problems to be solved by the present invention, reference is now made to FIGS. 9 to 11 which show three different examples of prior art thermal printing head.
A prior art thermal printing head shown in FIG. 9 comprises a support member 100 which carries a head circuit board 101. The support member 100 is made of an aluminum or aluminum alloy plate having a relatively large thickness. Thus, the support member itself is highly rigid. In use, the head circuit board 101 is held in contact with a platen 102 with thermosensitive paper interposed therebetween.
With the prior art arrangement of FIG. 9, the support member 100, which has a relatively large thickness, is usually prepared by drawing a material metal and then working the drawn plate. This manner of production is known to be rather costly, which problem is added by the relatively large thickness (i.e., large material amount) of the support member.
The cost problem itself may be reduced by utilizing a support member 110 which is formed by press-working a relatively thin steel plate, as shown in FIG. 10. The support member 110 is made to have reinforcing flanges along two longitudinal sides.
However, with the arrangement of FIG. 10, it is very difficult to realize strict surface flatness of the support member 110 over the entire length thereof when the support member is formed by press-working. On the other hand, the presence of the longitudinal reinforcing flanges imparts high rigidity to the support member. Thus, even if the support member is pressed by springs toward the platen 102, the head circuit board 101 carried on the support member cannot come into uniform contact with the platen due to bending reluctance of the support member, consequently resulting in deterioration in the printing quality.
It is conceivable to use a non-flanged thin steel plate 120 as a support member for the head circuit board 101, as shown in FIG. 11. In this case, the support member is easily bendable over the entire length thereof, and such flexibility is positively utilized to bring the head circuit board into uniform contact with the platen 102 under spring bias.
However, the prior art arrangement of FIG. 11 is disadvantageous in that the spring bias must be applied to the support member at a number of points in order to realize intimate contact over the entire length of the head circuit board 101, as indicated by arrows F. Thus, the require number of springs increases, and an apparatus (facsimile machine, printer, etc.) incorporating the printing head must be designed to have corresponding supports for the respective springs, consequently resulting in overall cost increase.